"Best" glide
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"Best" glide
In the past, I have drawn attention to my observation that for some aircraft, "best" glide speed may not be best for everything. Nearly all Flight Manuals present a best glide speed. This speed is presented to meet the certification requirement:
I have opined that arriving to short final/top of the flare at best glide speed as above, may result in disappointment, when one pulls to flare. If you have not stored speed (energy) with which to flare, your more steep than normal approach path might be impossible to fully arrest, and thump.
While bimbling around in the Super Cub this evening, I did some experimenting. (knowing that this Super Cub is an amateur built version, with no Flight Manual). While referring to the VSI and ASI, I glided. I glided at speeds from 50 MIAS to 75 MIAS. I was seeing rates of descent from 400 to 900 FPM. The experiment was to successfully "flare" at altitude, power off. Could I use the stored speed I had, to arrest the rate of descent? Knowing that VSI's lag, I figured that seeing a positive rate without adding power could be taken to mean that I had arrested the descent to zero, with a little extra time to judge a landing.
While gliding at 50 MPH, and 400 FPM, raising the nose to flare resulted in a VS reduction from -400 FPM to -300 FPM, not really enough to flare effectively, then the plane stalled. Gliding at 70 MPH and 800 FPM, I was able to arrest to zero FPM, and hold it a couple of seconds. 75 MPH and 900 FPM allowed a pull to achieve 150 FPM up for a second or so, so more than needed to flare.
I am therefore satisfied that gliding this plane at 50 MPH (not that there is a Flight Manual speed presented anyway) would result in a very heavy landing - so I did not try to the ground. My subsequent 8 power off touch and goes were generally flown 70 MPH short final to 60 MPH over the fence, and each resulted in a nice wheel landing.
If I had to make it to shore, I might glide at 55 to 60 MPH, but I would try to speed up to 70 MPH on final, and then hope to peep it on. I'll experiment with a couple of other types as I have to opportunity.
Sec. 23.71
[Glide: single-engine airplanes.]
[The maximum horizontal distance traveled in still air, in nautical miles, per 1,000 feet of altitude lost in a glide, and the speed necessary to achieve this must be determined with the engine inoperative, its propeller in the minimum drag position, and landing gear and wing flaps in the most favorable available position.]
[Glide: single-engine airplanes.]
[The maximum horizontal distance traveled in still air, in nautical miles, per 1,000 feet of altitude lost in a glide, and the speed necessary to achieve this must be determined with the engine inoperative, its propeller in the minimum drag position, and landing gear and wing flaps in the most favorable available position.]
While bimbling around in the Super Cub this evening, I did some experimenting. (knowing that this Super Cub is an amateur built version, with no Flight Manual). While referring to the VSI and ASI, I glided. I glided at speeds from 50 MIAS to 75 MIAS. I was seeing rates of descent from 400 to 900 FPM. The experiment was to successfully "flare" at altitude, power off. Could I use the stored speed I had, to arrest the rate of descent? Knowing that VSI's lag, I figured that seeing a positive rate without adding power could be taken to mean that I had arrested the descent to zero, with a little extra time to judge a landing.
While gliding at 50 MPH, and 400 FPM, raising the nose to flare resulted in a VS reduction from -400 FPM to -300 FPM, not really enough to flare effectively, then the plane stalled. Gliding at 70 MPH and 800 FPM, I was able to arrest to zero FPM, and hold it a couple of seconds. 75 MPH and 900 FPM allowed a pull to achieve 150 FPM up for a second or so, so more than needed to flare.
I am therefore satisfied that gliding this plane at 50 MPH (not that there is a Flight Manual speed presented anyway) would result in a very heavy landing - so I did not try to the ground. My subsequent 8 power off touch and goes were generally flown 70 MPH short final to 60 MPH over the fence, and each resulted in a nice wheel landing.
If I had to make it to shore, I might glide at 55 to 60 MPH, but I would try to speed up to 70 MPH on final, and then hope to peep it on. I'll experiment with a couple of other types as I have to opportunity.
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Are you comparing apples with apples there? Your experiments were related to minimum rate of descent, but the certification reference you have given is referring to maximum range. On the aircraft I fly the speed for max range is significantly higher than the speed for minimum rate of descent.
"Isn't his what glider pilots do, increase the approach speed a little for the hold-off and touchdown?"
Yes, Talkdownman.
We were taught to fly 1.5 stall speed plus half the wind velocity on the final.
Yes, Talkdownman.
We were taught to fly 1.5 stall speed plus half the wind velocity on the final.
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Would a power off approach to a wheeled landing not require more air speed than a power off full stall 3 pointer due to the angle of attack needed in the round out for a wheeler?
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Glider pilots used to, when I was into it, refer to L/D.
Which I thought meant best lift over drag. Or sink rate.
There were two different speeds, one to cover best distance over time, the other to lose least height over distance, I think, Though my memory may be wrong.
Which I thought meant best lift over drag. Or sink rate.
There were two different speeds, one to cover best distance over time, the other to lose least height over distance, I think, Though my memory may be wrong.
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Yes, in fairness, I neglected to qualify that my post is directed toward powerplane pilots. Not to exclude glider pilots, but I know things are a little different for unpowered aircraft. I am delighted to know that glider pilots complete power off approaches and power off landings every time. If power plane pilots were flying power off approaches, and power off landings, they might find new pleasure in honed skills.
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I do some glide approaches, and sometimes powered approaches. Certainly a busy airport circuit will not appreciate gliding approaches from downwind!
The OP mentions speed, as a consideration. This could be important whether gliding, or powering in. An engine failure in a single will force you to glide, and the choice of speed for that glide seems to be variable, based upon circumstances.
The OP mentions speed, as a consideration. This could be important whether gliding, or powering in. An engine failure in a single will force you to glide, and the choice of speed for that glide seems to be variable, based upon circumstances.
What weight were you flying at? Because i fly a 150 Cub, and glide approach at 50 knots is eminently possible to either a 3 point or a wheeler, solo and 60 litres (tug, half tanks or a bit less. Full is 135). Not a lot faster than you. Max weight i would use 55, both cases full flap, which on mine is 60 degrees. Most cubs have a bit less flap, mine was a crop duster and has some oddities. Short landing back of the drag curve and power five knots less. You might want to check the pitot static installation.
Bit of confusion here maybe.
Best Range Speed is the best TAS/Drag for the aeroplane.
Best Glide speed is Minimum Drag speed, usually a bit less than best TAS/Drag.
If the engine fails, then I would want to stay airborne as long as I can to sort out my priorities……. therefore Best Glide…….for the moment.
WHEN A PLAN HAS BEEN DECIDED, then you can go for Range if you need it. eg. to clear a wooded area or hilly ground.
When on final though, I still want a safe approach speed that is going to give me the least Ground Speed so that, if I can’t avoid hitting something then, at least, it will be with less energy.
With a Taildragger, as has been pointed out, WHEN YOU ARE SURE YOU ARE GOING TO MAKE IT, then you can use flap and/or sideslip with a few knots extra approach speed, to ensure a smooth flare to a THREEPOINT attitude.
This will give you a short ground run, reduce the chance of collision….. and maybe less blood…..
Just DON’T STRETCH THE GLIDE. If you are getting too low, carefully monitoring/adjusting your speed, RETRACT FLAP to reduce the ROD.
One other thing, remembering our gliding brethren, if the HW is strong and you don’t seem to be going anywhere, INCREASE THE NOSEDOWN ATTITUDE TO INCREASE YOUR SPEED. This will increase PENETRATION and, once you are in with a chance again, adjust your approach speed as necessary. Remember that, in this case, your GROUND SPEED will be lower because of the stronger HW and therefore the ground run will still be short even after a bit of float.
Lecture over…… sorry. Hope it helps.
Best Range Speed is the best TAS/Drag for the aeroplane.
Best Glide speed is Minimum Drag speed, usually a bit less than best TAS/Drag.
If the engine fails, then I would want to stay airborne as long as I can to sort out my priorities……. therefore Best Glide…….for the moment.
WHEN A PLAN HAS BEEN DECIDED, then you can go for Range if you need it. eg. to clear a wooded area or hilly ground.
When on final though, I still want a safe approach speed that is going to give me the least Ground Speed so that, if I can’t avoid hitting something then, at least, it will be with less energy.
With a Taildragger, as has been pointed out, WHEN YOU ARE SURE YOU ARE GOING TO MAKE IT, then you can use flap and/or sideslip with a few knots extra approach speed, to ensure a smooth flare to a THREEPOINT attitude.
This will give you a short ground run, reduce the chance of collision….. and maybe less blood…..
Just DON’T STRETCH THE GLIDE. If you are getting too low, carefully monitoring/adjusting your speed, RETRACT FLAP to reduce the ROD.
One other thing, remembering our gliding brethren, if the HW is strong and you don’t seem to be going anywhere, INCREASE THE NOSEDOWN ATTITUDE TO INCREASE YOUR SPEED. This will increase PENETRATION and, once you are in with a chance again, adjust your approach speed as necessary. Remember that, in this case, your GROUND SPEED will be lower because of the stronger HW and therefore the ground run will still be short even after a bit of float.
Lecture over…… sorry.
Hope it helps.
Much better a good approach to a poor field you can make than a poor approach to a good field you can't make
I doubt minimum sink speed speed in a SEP with dead engine will buy more than several seconds in the way of think time.
Turning downwind and slowing down to a few kt below best glide will give you the most selection of fields - caveat that you're not over hostile terrain in which case you are advised to know exactly where you can find decent landing opportunities.
Gliders do have an advantage over hilly terrain compared to engined aircraft as a 40+ glide ratio can take you a long way over hostile terrain.
I doubt minimum sink speed speed in a SEP with dead engine will buy more than several seconds in the way of think time.
Turning downwind and slowing down to a few kt below best glide will give you the most selection of fields - caveat that you're not over hostile terrain in which case you are advised to know exactly where you can find decent landing opportunities.
Gliders do have an advantage over hilly terrain compared to engined aircraft as a 40+ glide ratio can take you a long way over hostile terrain.
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Sorry to spoil your Parade, but.... I think your original tests may only be valid at one condition. Maybe with the C of G in a more rearward position you could have got a better pitch attitude change.
Also when you pulled up (to flair), did you pull abruptly to the back-stop i.e momentarily flew beyond the Stall ?
Mathematically Vx and Vy are linked, as the minimum sink speed occurs at minimum Drag, and this Drag is made up of the Sum of a Square function and an Inverse-Square function. Without going into the Differential Calculus, Vx is always about 80% of Vy.
Also when you pulled up (to flair), did you pull abruptly to the back-stop i.e momentarily flew beyond the Stall ?
Mathematically Vx and Vy are linked, as the minimum sink speed occurs at minimum Drag, and this Drag is made up of the Sum of a Square function and an Inverse-Square function. Without going into the Differential Calculus, Vx is always about 80% of Vy.
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If you are getting too low, carefully monitoring/adjusting your speed, RETRACT FLAP to reduce the ROD.
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One other thing, remembering our gliding brethren, if the HW is strong and you don’t seem to be going anywhere, INCREASE THE NOSEDOWN ATTITUDE TO INCREASE YOUR SPEED. This will increase PENETRATION and, once you are in with a chance again,
